Abstract: Objective To explore the relationship among physical activity,screen time and 20-meter shuttle run test (20 m SRT) performances among children and adolescents of Han ethnicity,and to provide a basis for promoting the development of cardiorespiratory fitness of Chinese children and adolescents.Methods A total of 12 221 children and adolescents aged 10-18 years of Han ethnicity were chosen by the random case method from six administrative regions,and the association among their physical activity,screen time and 20 m SRT were explored.Results The detection rate of high-grade 20 m SRT performances among girls of positive means of transportation was significantly higher than that in girls of passive means of transportation (x2 =5.753,P<0.05).The prevalence of high-grade 20 m SRT performances among children with exercise time more than 60 min/d was significantly higher than that of children with exercise time <30 min/d,30-60 min/d(P<0.05).The prevalence of high-grade 20 m SRT performances among children of screen time(>2 h/d) was significantly lower than that of children of screen time(< 1 h/d,1-2 h/d) (P<0.05).Logistic regression analysis showed that exercise time above 60 min/d(OR =1.65) and East China(OR =4.24) were protective factors of 20 m SRT performances among Han children and adolescents in China,and screen time above 2 h/d (OR =0.84) was the risk factor.Conclusion Physical activity status(exercise time >60 min/d) is independently associated with higher cardiorespiratory fitness of Chinese children and adolescents of Han ethnicity.However,the more screen time was associated with lower cardiorespiratory fitness.